Power generation from waterways and coastal currents is well-known and commonly practiced in coastal waters and rivers. A well-known application is in dams with built-in turbines driving generators for the production of electric power. Most navigable waterways have a controlled water level to facilitate shipping by maintaining minimum depths through the placement of dams in the waterway. Shipping is made possible through the location of locks adjacent to the dams.
The Mississippi River is an example of such a waterway with a controlled water level and a system of dams with locks. The water drop at most dams is 20 feet or less. One dam and lock has a drop of 38 feet and has been provided with a hydroelectric power plant taking power from the waterway. The 38 feet of static head provides an opportunity to produce power efficiently since the head is substantially greater than the other dams in this waterway. The static head in all other dams was not sufficient to provide a return-on-investment for a conventional hydroelectric power plant in conjunction with these dams.
The placement of dams also reduces and evens out the speed of the water flow, a benefit for the waterway shipping industry. Since flowing water has kinetic energy, it can also be used for power generation. However, the power level of an in-stream power-generating system is much smaller than what can be generated by a static-head-type turbine as mentioned above.
Both low-static-head and in-stream systems have traditionally not attracted interest because the cost of building the conventional equipment to generate this power was very high in relation to the benefit of the power produced. The present invention reduces the cost of the power-generating equipment to such a low level that power can now be efficiently and cost-effectively produced using existing dams with low static heads as well as waterways with a current.
Traditional generating systems consist of a turbine placed on a base, and the turbine is connected to a generator via a shaft and a coupling placed on that same base. In the case of an in-stream turbine, the turbine is suspended under a float with the electric generator, usually driven by a belt, placed on the float (where it is dry). The presence of a float makes it vulnerable to debris, waves and ice in a waterway as well as adding cost. The present invention lowers the cost of such an in-stream system such that it becomes economically feasible to generate electric power in this fashion. Also, the method of installation of such a system is greatly simplified. This invention allows efficient, low-cost power generation for both low-pressure static-head and in-stream systems that are not possible with conventional systems.
The cost reduction is accomplished by integrating the turbine and the electric power generator in one compact unit made of composite materials to keep both cost and weight low. It is modular in design, allowing combinations of components to select a match for the power requirement of a given application. It fits in-line with water ducts for easy installation and maintenance. It is submersible and can be suspended in a water current in ways that are not possible or practical with a separate turbine and generator.
Most conventional hydroelectric power generation systems do not have the capability of reversing the operation and turning the power generation system into a pumping system by applying an electric current to the generator. The present invention allows the electric generator to become an electric motor by reversing its function by changing the electronic commutation. The axial flow turbine functions equally well as a pump so that the inventive system can be used to store energy by applying to the unit electric power to be stored and pumping water from one reservoir to a higher-elevation reservoir. When the electronic commutation is reversed once again, it turns the power system back into a generator and so can recover the stored power. Therefore, unlike most conventional hydroelectric power generators, the present invention can be used as an energy storage and recovery system.